Method of constructing concrete floating body for floating type offshore wind power generation facility

Abstract

[Problem] To improve the efficiency of assembly work by saving labor required for tensioning and anchoring work of PC steel material in a method of constructing a concrete floating body. [Solution] PC steel materials 19 are sorted in advance into a group of PC steel rods 20 to be used for temporarily assembling precast cylindrical bodies in order, and a group of PC steel strands 23 to be used for introducing predetermined tension after completing temporary assembly of a concrete floating body. In a temporary assembly step of a concrete floating body 4A, the temporary assembly of the concrete floating body 4A is completed by assembling all precast cylindrical bodies 15 while introducing tension to the PC steel rods 20 and anchoring the group of PC rods 20, each time the precast cylindrical bodies 15 are connected sequentially, and installing a floating body bottom part 29 on the endmost part. In a tension introduction step, the PC steel strands 23 are inserted in the longitudinal direction over the entire length of the concrete floating body 4A, and introduction of tension to the PC steel strands 23 and anchoring are performed for the group of PC steel strands 23.

Description

Title of Invention: METHOD OF CONSTRUCTING CONCRETE FLOATING BODY FOR FLOATING TYPE OFFSHORE WIND POWER GENERATION FACILITY Technical Field

[0001] The present invention relates to a method of efficiently constructing a concrete floating body in a floating offshore wind power generation facility having a concrete floating body formed by stacking a plurality of concrete precast cylindrical bodies in multiple stages in a height direction and tightly connecting the respective precast cylindrical bodies by PC steel materials to integrate the precast cylindrical bodies with one another. Background Art

[0002] Conventionally, power generation methods, such as hydroelectric power generation, thermal power generation, and nuclear power generation, have mainly been adopted, and, in recent years, wind power generation that generates electricity using natural wind has attracted attention from the viewpoints of environment and effective use of natural energy. Such wind power generation facilities include on-land installation type and water installation (mainly sea installation) type facilities, and, in the case of Japan, having mountainous terrain from coastal areas to inland areas, there are few plains in coastal areas where stable winds can be expected.  On the other hand, Japan is surrounded by sea on all four sides and thus is advantageous in that it is possible to easily obtain winds suitable for power generation at sea and, at the same time, there is little or no restriction on installation thereof. Therefore, in recent years, various types of offshore wind power generation facilities and floating body structures have been frequently proposed.

[0003] The floating structures are broadly classified into a barge-type floating body in which a floating body is floated on the water surface, a semi-submersible type floating body in which a floating body is floated in a semi-submerged state with the lower portion submerged below the water surface, and a spar-type floating body in which a floating body is floated in an upright position like a fishing float.

[0004] With regard to the spar-type floating body, the present applicant has proposed, in the following Patent Literature 1, an offshore wind power generation facility (hereinafter referred to as a spar-type offshore wind power generation facility) including a floating body, a mooring cable, a tower, and a nacelle and a plurality of windmill blades provided at the top of the tower, wherein the floating body has a spartype floating body structure including a lower concrete floating body structure (hereinafter referred to as a concrete floating body) including a plurality of concrete precast cylindrical bodies stacked on top of each other in a height direction and tightly connected to each other with a PC steel material, and an upper steel floating body structure (hereinafter referred to as a steel floating body) consecutively provided above the concrete floating body.

[0005] As a method of constructing the floating body of the spar-type offshore wind power generation facility, the steel floating body and the concrete floating body are assembled in a horizontally laid-down state at a quay yard to complete the floating body (refer to Patent Literature 2 listed below).

[0006] In particular, in the assembly of the concrete floating body, as shown in Fig. 11, since the concrete floating body is constructed in a horizontally orientated state, the precast cylindrical body 50 manufactured in a vertically oriented state with their axial directions oriented in the vertical direction is erected so as to be in a horizontally oriented state, and then the erected precast cylindrical body 60 is lifted by a crane and sequentially connected to an end portion of an assembled group of precast cylindrical bodies 61, thereby performing the assembly.

[0007] In order to connect the precast cylindrical body 60 to an end portion of the assembled concrete floating body 61, all of a large number of the PC steel materials disposed over the entire circumference of the precast cylindrical body are configured as PC steel rods 62, 62 ., and, as shown in Fig. 12, for all the PC steel rods 62, each time the precast cylindrical body 60 is sequentially connected thereto, all the precast cylindrical bodies 61 are assembled while introducing tensioning force into and anchoring all the PC steel rods 62. Citation List Patent Literature

[0008] Patent Literature 1: Japanese Patent No. 5274329 Patent Literature 2: Japanese Patent Application Laid-Open Publication No. 2018-173011 Summary of Invention Technical Problem

[0009] As described above, the concrete floating body is assembled by a procedure of performing tensioning and anchoring for all the PC steel rods 62,  62  ... in the circumferential direction inserted through the precast cylindrical body 60, for each precast cylindrical body 60. Accordingly, since the number of times of tensioning and anchoring the PC steel materials 62 performed when assembling the precast cylindrical bodies 61 is enormous, a lot of time and effort have been required to assemble the precast cylindrical bodies 61, 61 .. For example, in the example shown in Fig. 12, assuming the number of PC steel rods 62 per a cross section of the precast cylindrical body 60 is 44 and the number of precast cylindrical bodies 60 to be assembled is 10, tensioning and anchoring of the PC steel rods 62 have been performed as many as 440 times (44 rods x 10 bodies = 440).

[0010] Accordingly, a main problem of a present invention is to improve the efficiency of assembly work of the precast cylindrical body by saving labor required for tensioning and anchoring work of the PC steel material, in a method of constructing a concrete floating body for a floating type offshore wind power generation facility having a concrete floating body formed by connecting a plurality of precast cylindrical bodies, and tightly connecting and integrating the respective precast cylindrical bodies with a large number of PC steel materials. Solution to Problem

[0011] In order to solve the above-described problem, as the present invention according to claim 1, provided is a method of constructing a concrete floating body for a floating type offshore wind power generation facility having a concrete floating body formed by connecting a plurality of precast cylindrical bodies, and tightly connecting and integrating the respective precast cylindrical bodies with a large number of PC steel materials, the method including: in advance, sorting a large number of PC steel materials disposed over an entire circumference of the precast cylindrical body into a group of PC steel rods used for temporarily assembling the precast cylindrical bodies in order, and a group of PC steel strands used for introducing a predetermined tensioning force after completing temporary assembly of the concrete floating body; in a temporary assembly step of the concrete floating body, completing temporary assembly of the concrete floating body by assembling all the precast cylindrical bodies while introducing tensioning force into the PC steel rods and anchoring the PC steel rods, in the group of PC steel rods each time the precast cylindrical bodies are sequentially connected, and installing a floating body bottom portion at an endmost portion; and in a tensioning force introduction step, in the group of PC steel strands, inserting the PC steel strands in a longitudinal direction over the entire length of the concrete floating body, and introducing tensioning force into the PC steel strands and anchoring the PC steel strands.

[0012] In the invention according to claim 1, in constructing the concrete floating body, in advance, a large number of PC steel materials disposed over an entire circumference of the precast cylindrical body are divided into a group of PC steel rods used for temporarily assembling the precast cylindrical bodies in order, and a group of PC steel strands used for introducing a predetermined tensioning force after completing temporary assembly of all the precast cylindrical bodies.

[0013] The group of PC steel rods is a PC steel material for temporarily assembling a predetermined number of precast cylindrical bodies to construct the concrete floating body, and PC steel rods capable of being tensioned and anchored for each precast cylindrical body are used. In the temporary assembly step of the precast cylindrical bodies, each time the precast cylindrical bodies are sequentially connected, in the group of PC steel rods, tensioning force is introduced into and anchoring is performed for the PC steel rods, while temporarily assembling all the precast cylindrical bodies and installing the floating body bottom portion at an endmost portion, thereby completing temporary assembly of the concrete floating body.

[0014] Meanwhile, the PC steel strands are used for the PC steel material arrangement portions other than the PC steel rods.   In the tensioning force introduction step after completing the temporary assembly of the concrete floating body, in the group of PC steel strands, the PC steel strands are inserted in a longitudinal direction over the entire length of the concrete floating body, and the introduction of tensioning force into the PC steel strands and the anchoring of the PC steel strands are performed. Since the PC steel strands are inserted in a longitudinal direction into the concrete floating body for which temporary assembly has been completed and then tensioning force is introduced, the introduction of tensioning force and the anchoring only need to be performed once, thereby making it possible to save labor in the prestress introduction and anchoring work.

[0015] Moreover, since the tensioning force input per one PC steel material can be set larger for the PC steel strands than for the PC steel rods, it becomes possible to expect further labor saving in the prestress introduction and anchoring work by reducing the number of PC steel materials.

[0016] As the present invention according to claim 2, provided is the method of constructing the concrete floating body for the floating type offshore wind power generation facility according to claim 1, wherein, in the temporary assembly step of the concrete floating body, the group of PC steel rods is determined such that a compressive stress intensity of a bonded surface between the precast cylindrical bodies is set to 0.2 to 0.4 N / mm2, and the remainder is determined as the group of PC steel strands.

[0017] The invention according to claim 2 described above defines a method for determining the number of the PC steel rods in the group of PC steel rods. As described later, according to the “Design and Construction Standard for External Cable Structure and Precast Segment Method,” it is specified that, when bonding segments, a compressive stress of about 0.3 N / mm2 is to be applied until the epoxy resin is cured.    In accordance with this specification, in the temporary assembly step of the concrete floating body, the number of the group of PC steel rods is determined such that a compressive stress intensity of a bonded surface between the precast cylindrical bodies is set to 0.2 to 0.4 N / mm2, and the remainder is determined as the group of PC steel strands.

[0018] As the present invention according to claim 3, provided is the method of constructing the concrete floating body for the floating type offshore wind power generation facility according to claim 1, wherein the precast cylindrical body is formed into a cylindrical body by assembling a plurality of arcuate divided precast members divided in a circumferential direction, and the group of PC steel rods is determined to include at least two locations, one location on each of both sides, in each arcuate divided precast member, on condition that a compressive stress intensity of a bonded surface between the precast cylindrical bodies is set to 0.2 to 0.4 N / mm2, and the remainder is determined as the group of PC steel strands.

[0019] The invention according to claim 3 described above defines a method for determining the number of the group of PC steel rods in a divided type in which the precast cylindrical body is formed into a cylindrical body by assembling a plurality of arcuate divided precast members divided in a circumferential direction. In this case, on condition that a compressive stress intensity of a bonded surface between the precast cylindrical bodies is set to 0.2 to 0.4 N / mm2, in order to securely and well-balancedly fix each arcuate divided precast member, the number of the group of PC steel rods is determined to include at least two locations, one location on each of both sides, in each arcuate divided precast member, and the remainder is determined as the group of PC steel strands.

[0020] As the present invention according to claim 4, provided is the method of constructing the concrete floating body for the floating type offshore wind power generation facility according to any one of claims 1-3, wherein the precast cylindrical bodies are sequentially connected to one another in a horizontal direction in a horizontally orientated state, or sequentially connected to one another in a height direction in a vertically oriented state.

[0021] In the invention according to claim 4 described above, in constructing the concrete floating body, as a direction in which the precast cylindrical bodies are connected, horizontal construction in which a plurality of the precast cylindrical bodies are connected to one another in a lateral direction to construct the concrete floating body in a horizontally laid-down state may be employed, or vertical construction in which a plurality of the precast cylindrical bodies are connected to one another in a height direction to construct the concrete floating body in an erected state may be employed. Advantageous Effects of Invention

[0022] As described in detail above, according to the present invention, in a method of constructing a concrete floating body for a floating type offshore wind power generation facility having a concrete floating body formed by connecting a plurality of precast cylindrical bodies, and tightly connecting and integrating the respective precast cylindrical bodies with a large number of PC steel materials, it is possible to improve the efficiency of assembly work of the precast cylindrical body by saving labor required for tensioning and anchoring work of the PC steel material. Brief Description of Drawings

[0023] [Fig. 1]    Fig. 1 is an overall view of a spar-type offshore wind power generation facility 1. [Fig. 2]    Fig. 2 is a longitudinal sectional view of a floating body 4. [Fig. 3]    Fig. 3 is a perspective diagram showing a construction procedure of the spar-type offshore wind power generation facility 1. [Fig. 4]    Fig. 4 is a schematic diagram showing connection between the precast cylindrical bodies 15 when constructing a concrete floating body 4A in a horizontally orientated state. [Fig. 5]    Fig. 5 shows the precast cylindrical body 15, in which Fig. 5(A) is a front view, Fig. 5(B) is a sectional view taken in the line B-B of Fig. 5(A), and Fig. 5(C) is a sectional view taken in the line C-C of Fig. 5(A). [Fig. 6] Fig. 6 is a schematic diagram showing connection between the precast cylindrical bodies 15 in a temporary assembly step. [Fig. 7] Fig. 7 is a schematic diagram showing connection between the precast cylindrical bodies 15 by a PC steel rod 20 (Figs. 7(A) and 7(B)). [Fig. 8] Fig. 8 is a schematic diagram showing forming of a sheath hole at a location where a PC steel strand are to be arranged, in the temporary assembly step (Figs. 8(A) and 8(B)). [Fig. 9] Fig. 9 is a longitudinal sectional view of the concrete floating body 4A in which temporary assembly of the precast cylindrical bodies 15, 15 ... and a precast bottom plate 29 has been completed. [Fig. 10] Fig. 10 is a schematic diagram showing insertion of the PC steel strand 23, in a tensioning force introduction step. [Fig. 11] Fig. 11 is a schematic diagram showing connection between the precast cylindrical bodies 60. [Fig. 12] Fig. 12 is a front view diagram of a conventional precast cylindrical body 60 (view taken in the line XII-XII of Fig. 11). Description of Embodiments

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0025] [Hybrid Spar-Type Offshore Wind Power Generation Facility 1] First, a spar-type offshore wind power generation facility 1 to which the present invention is applied will be described in detail on the basis of Figs. 1 and 2.

[0026] The spar-type offshore wind power generation facility 1 is, as shown in Fig. 1, configured by a spar-type cylindrical floating body 4, mooring cables 5, 5 ., a tower 6, and a windmill 7 including a nacelle 8 and a plurality of blades 9, 9 ... provided at a top portion of the tower 6.

[0027] The floating body 4, as shown in Fig. 2, includes a concrete floating body 4A formed by stacking a plurality of concrete precast cylindrical bodies 15, 15 . (hereinafter referred to as a "concrete ring 15") in a height direction and tightly connecting the respective precast cylindrical bodies 15,  15  . by PC steel materials 19,  19  . to be integrated with one another, and a steel floating body 4B consecutively provided above the concrete floating body 4A.

[0028] Ballast materials such as water, gravels, fine aggregates or coarse aggregates, metal particles, or the like can be introduced into or discharged from a hollow portion of the floating body 4, thereby making it possible to adjust buoyancy (draft). The introduction / discharge of the ballast materials can be realized by adopting a fluid transportation method previously proposed by the present applicant in Japanese Patent Application Laid-Open Publication No. 2012-201217.

[0029] The concrete floating body 4A is composed of concrete precast cylindrical bodies 15, 15 ... and floating body bottom portions 29. The precast cylindrical bodies 15 are circular cylindrical precast members having the same cross section in an axial direction, and a hollow precast member fabricated by using the same formwork for each member or manufactured by centrifugal molding is used.

[0030] Sheaths 21, 21 . for passing the PC steel materials 19,  19 . therethrough are embedded in a side wall of the precast cylindrical body 15. The PC steel materials 19 and the sheaths 21 will be described later in more detail.

[0031] Meanwhile, the steel floating body 4B is composed of a steel cylindrical body 17 relatively located on a lower side and a steel cylindrical body 18 relatively located on an upper side.    A lower portion of the lower steel cylindrical body 17 has the same outer diameter dimension as the precast cylindrical body 15, and the lower steel cylindrical body 17 is connected to the precast cylindrical body 15 by bolts, welding, or the like (bolt fastening is shown in the illustrated example), as shown in Fig. 5. An upper portion of the steel cylindrical body 17 has a truncated conical shape with a gradually narrowed diameter.

[0032] The upper steel cylindrical body 18 is a cylindrical body having an outer diameter dimension continuous with an upper outer diameter of the lower steel cylindrical body 17, and is connected to the lower steel cylindrical body 17 by bolts, welding, or the like (bolt fastening is shown in the illustrated example).  These steel cylindrical bodies 17, 18 are composed of respective steel rings divided for each predetermined weight, and the respective steel rings are integrated by being circumferentially welded.

[0033] The tower 6 is composed of steel material, concrete, or prestressed reinforced concrete (PRC), but it is preferable to use one manufactured of steel material so as to reduce the total weight. The outer diameter of the tower 6 and the outer diameter of the upper steel cylindrical body 18 substantially coincide with each other, and the outer shape is continuous in the vertical direction without any step or the like.

[0034] As shown in Fig. 1, a mooring point P of the mooring cable 5 to the floating body 4 is set at a position below the sea surface and higher than a center of gravity G of the floating body 4. Accordingly, it becomes possible to prevent ships and vessels from coming into contact with the mooring cable 5. Moreover, since a resisting moment centered on the center of gravity G of the floating body 4 is generated at the mooring point P so as to suppress excessive tilting of the floating body 4, it becomes possible to appropriately maintain a tilted posture state of the tower 6.

[0035] The nacelle 8 is a device equipped with a generator for converting rotation of the windmill 7 into electricity, a controller capable of automatically changing an angle of the blades 9, and the like.

[0036] [Construction Method of Floating Body 4] As a method of constructing the floating body for completing the floating body 4 in a horizontally oriented state in which the floating body 4 is horizontally laid down at a quay yard, it is possible to suitably adopt the method according to the invention disclosed in Japanese Patent Application Laid-Open Publication No. 2018-173011 proposed by the present applicant.

[0037] As shown in Fig. 3, in the floating body construction method, a steel ring connecting yard A, a concrete ring fabricating yard B, and a concrete ring connecting yard C are defined and provided in the quay yard.

[0038] In the steel ring connecting yard A, a first gantry crane 50 is provided so as to be travelable in a predetermined direction, rotating-function-equipped stands 52,  52  ... are installed at appropriate intervals in a traveling direction of the first gantry crane, and a mobile tent 56 movable in the traveling direction of the first gantry crane is provided. In the concrete ring fabricating yard B, a mobile tent 57 is provided, and a complete set of concrete ring manufacturing facilities is installed. In the concrete ring connecting yard C, a second gantry crane 55 is provided so as to be movable in a predetermined direction, and a mobile tent 58 movable in a traveling direction of the second gantry crane is provided.

[0039] The floating body construction method includes: a first process of sequentially installing the steel rings 51, 51 ... on the rotating-function-equipped stands 52, 52 ... by using the first gantry crane 50, covering the surroundings with the mobile tent 56 as necessary, and circumferentially welding and connecting the steel rings 51, 51 . while rotating the steel rings 51, 51 . around an axis, thereby completing the steel floating body 53B; and a second process of, once the steel floating body 53B is moved to the concrete ring connecting yard C and installed at a predetermined position, transporting the concrete rings 15 fabricated in the concrete ring fabricating yard B to the concrete ring connecting yard C in sequence, covering the surroundings with the mobile tent 58 as necessary, and connecting the concrete rings 15 to the steel floating body 53B in succession by using the second gantry crane 55 and tightly connecting and integrating the concrete rings 15 by PC steel material 19, thereby completing the floating body 53.

[0040] [Construction Method of Concrete Floating Body 4A] <Preparation Procedure> In the preparation procedure, in advance, a large number of PC steel materials 19, 19 ... disposed over an entire circumference of the precast cylindrical body 15 are sorted into a group of PC steel rods 20, 20 . used for temporarily assembling the precast cylindrical bodies 15 in order, and a group of PC steel strands 23, 23 . used for introducing a predetermined tensioning force after completing temporary assembly of the concrete floating body 4A.

[0041] Specifically, describing the precast cylindrical body 15 shown in Fig. 5, the precast cylindrical body 15 is formed into a cylindrical body by assembling arcuate divided precast members 16A to 16H divided into eight sections in a circumferential direction. Sheaths 21, 21 . for a large number of PC steel materials 19,  19 . to be installed at predetermined intervals over an entire circumference are embedded in a wall surface of the precast cylindrical body 15.

[0042] For setting the group of PC steel rods 20,  20 ., according to the "Design and Construction Standard for External Cable Structure and Precast Segment Method," edited by the Japan Prestressed Concrete Institute, it is specified that, when bonding segments, a compressive stress of about 0.3 N / mm2 is to be applied until the epoxy resin is cured (Chapter 9, Examination During Construction,   9.3, Examination at the Time of Bonding). In accordance with this guideline, in the temporary assembly step of the precast cylindrical body 15, it is preferable to determine the number of the PC steel rods 20,  20 ... in the group such that a compressive stress intensity of a bonded surface between the precast cylindrical bodies 15, 15 is set to 0.2 to 0.4 N / mm2, preferably within a range of 0.25 to 0.35 N / mm2.

[0043] Accordingly, in the precast cylindrical body 15 shown in Fig. 5, among all the PC steel materials 19, 19 ., the group of PC steel rods 20,  20  . used for temporarily assembling the precast cylindrical bodies 15 in order is set so as to include two locations in total, one location on each of both sides, in each of the arcuate divided precast members 16A to 16H, on condition that a compressive stress intensity of the bonded surface between the precast cylindrical bodies 15, 15 is set to within a range of 0.2 to 0.4 N / mm2. When the size of the precast cylindrical body 15 is increased and the compressive stress intensity of the bonded surface between the precast cylindrical bodies 15, 15 falls below the range of 0.2 to 0.4 N / mm2 by providing a total of only two locations, one location on each of both sides, in each of the arcuate divided precast members 16A to 16H are configured as the PC steel rods 20, 20, locations including one or more intermediate PC steel rods added between the respective locations on each of both sides in each of the arcuate divided precast members 16A to 16H may be configured as the PC steel rods 20, 20 ..

[0044] As shown in Fig. 5(C), in the sheath 21 at a location where the PC steel rods 20 are disposed, a sheath enlarged-diameter portion 21a (coupler sheath) is formed at a lower end portion of each the sheath 21, 21 ... so as to be capable of accommodating a nut member 25 for anchoring the PC steel rod 19 and a coupler 26 for connecting the PC steel rods to one another, and a box-out portion 22 for fitting an anchor plate for anchoring is formed at an upper portion thereof. Since the total number of the PC steel materials 19, 19 . is 72 and the number of the PC steel rods 20 is 16, the PC steel rods 20, 20 . account for about 22% of the total number.

[0045] Meanwhile, all the PC steel materials other than the group of PC steel rods 20, 20 . serve as the group of PC steel strands 23, 23 .. As shown in Fig. 5(B), as for the sheaths 21 at locations where the PC steel strands 23, 23 . are disposed, the sheaths 21 having the same diameter over the entire length in the height direction are respectively embedded at the locations where the PC steel strands 23 are disposed.

[0046] <Temporary Assembly Step of Concrete Floating Body 4A> In the construction of the concrete floating body 4A, first, as shown in Fig. 6, a temporary assembly step is performed by sequentially connecting the precast cylindrical bodies 15, 15 . in a horizontal direction in a horizontally oriented state. In this temporary assembly step, among all the PC steel materials 19, 19 ., only the group of PC steel rods 20, 20 ... is used.

[0047] When sequentially connecting the precast cylindrical body 15 to be attached to an end face of the installed precast cylindrical bodies 15,  15  ., the connection is performed in a state in which the positions of the PC steel rods 20 are aligned with one another. Then, as shown in Fig. 7(A), when the precast cylindrical body 15 is disposed adjacent to the assembled concrete floating body while the PC steel rods 20, 20 . extending from the assembled concrete floating body are respectively inserted through the sheaths 21, 21 ., an anchor plate 24 is fitted into the box-out portion 22, and prestress is introduced into the PC steel rods 20 and anchoring is performed by the nut member 25, thereby achieving the integration.

[0048] Next, as shown in Fig. 7(B), when a coupler 26 is screwed onto a protruding portion of the PC steel rod 20 and the next PC steel rod 20 is connected to one another, the next precast cylindrical body 15 on the attaching side is disposed adjacent thereto while inserting the PC steel rod 20 into the sheaths 21, 21 . of the next precast cylindrical body 15, and the precast cylindrical bodies 15 are sequentially assembled in a longitudinal direction by the procedure of tensioning and anchoring the PC steel rod 20 in the manner described above. Note that a grout material is injected into the sheath 21 through a grout injection hole 27.

[0049] At the bonded surface between the assembled precast cylindrical body 15 and the precast cylindrical body 15 on the attaching side, gaskets 28 are disposed one each at inner and outer positions in order to ensure water-tightness and bonding of the mating surfaces, and an adhesive such as an epoxy resin-based adhesive is applied to the bonded surface.

[0050] Meanwhile, at locations where the PC steel strands 23, 23 ... are to be disposed, as shown in Fig. 8, the sheaths 21, 21 are aligned so as to be continuous in a longitudinal direction, thereby forming an elongated space for inserting the PC steel strands 23 in a subsequent tensioning force introduction step.

[0051] As shown in Fig. 9, when the connection of all the precast cylindrical bodies 15,  15 . is completed and the precast bottom plate 29 is connected to an endmost portion, temporary assembly of the concrete floating body 4A is completed.

[0052] <Tensioning Force Introduction Step> In the tensioning force introduction step after completing the temporary assembly of the concrete floating body 4A, in each group of PC steel strands 23, 23 ., the PC steel strands 23 are inserted therethrough in a longitudinal direction over the entire length of the concrete floating body 4A, and tensioning force is introduced into the PC steel strands 23 and the PC steel strands 23 are anchored.

[0053] Specifically, as shown in Fig. 10, the PC steel strand 23 is paid out from a reel 30 around which the PC steel strand 23 is wound, and is inserted into the sheath 21 for the PC steel strand 23 of the concrete floating body 4A. Then, introducing the tensioning force to the PC steel strand 23 and anchoring thereof are performed between both end portions of the concrete floating body 4A. Moreover, a grout material is injected into the sheath 21. These works are performed for all PC steel strands 23 and 23 ., thereby completing the concrete floating body 4A.

[0054] [Other Embodiments] (1) The above-described embodiment is directed to a spar-type floating body in which the floating body 4 comprises the concrete floating body 4A and the steel floating body 4B consecutively provided above the concrete floating body 4A. However, even in the case of a spar-type floating body in which the floating body 4 comprises only the concrete floating body 4A formed by stacking a plurality of precast cylindrical bodies 15, 15 ... in multiple stages over the entire length and tightly connecting the respective precast cylindrical bodies 15, 15 . by the PC steel material 19 to integrate the concrete rings 15, 15 . with one another, it is possible to construct the floating body 4 in the same procedure.

[0055] (2) In the above-described embodiment, the precast cylindrical bodies 15,  15 ... are sequentially connected to one another in a horizontal direction in a horizontally oriented state to be completed, but the precast cylindrical bodies 15, 15 . may be sequentially connected to one another in a height direction in a vertically oriented state. Reference Signs List

[0056] 1: Spar-type offshore wind power generation facility; 4: Floating body; 4A: Concrete floating body; 4B:  Steel floating body; 5: Mooring cable; 6: Tower; 7: Windmill; 8: Nacelle; 9: Blade; 15: Precast cylindrical body (concrete ring); 19: PC steel material; 20: PC steel rod; 21: Sheath; 23: PC steel strand; and 29: precast bottom plate.

Claims

1. A method of constructing a concrete floating body for a floating type offshore wind power generation facility having a concrete floating body formed by connecting a plurality of precast cylindrical bodies, and tightly connecting and integrating the respective precast cylindrical bodies with a large number of PC steel materials, the method including:in advance, sorting a large number of PC steel materials disposed over an entire circumference of the precast cylindrical body into a group of PC steel rods used for temporarily assembling the precast cylindrical bodies in order, and a group of PC steel strands used for introducing a predetermined tensioning force after completing temporary assembly of the concrete floating body;in a temporary assembly step of the concrete floating body, completing temporary assembly of the concrete floating body by assembling all the precast cylindrical bodies while introducing tensioning force into the PC steel rods and anchoring the PC steel rods, in the group of PC steel rods each time the precast cylindrical bodies are sequentially connected, and installing a floating body bottom portion at an endmost portion; andin a tensioning force introduction step, in the group of PC steel strands, inserting the PC steel strands in a longitudinal direction over the entire length of the concrete floating body, and introducing tensioning force into the PCsteel strands and anchoring the PC steel strands.

2. The method of constructing the concrete floating body for the floating type offshore wind power generation facility according to claim 1, wherein in the temporary assembly step of the concrete floating body, the group of PC steel rods is determined such that a compressive stress intensity of a bonded surface between the precast cylindrical bodies is set to 0.2 to 0.4 N / mm2, and the remainder is determined as the group of PC steel strands.

3. The method of constructing the concrete floating body for the floating type offshore wind power generation facility according to claim 1, wherein the precast cylindrical bodyis formed into a cylindrical body by assembling a plurality of arcuate divided precast members divided in a circumferential direction, and the group of PC steel rods is determined to include at least two locations, one location on each of both sides, in each arcuate divided precast member, on condition that a compressive stress intensity of a bonded surface between the precast cylindrical bodies is set to 0.2 to 0.4 N / mm2, and the remainder is determined as the group of PC steel strands.

4. The method of constructing the concrete floating bodyfor the floating type offshore wind power generation facility according to any one of claims 1-3, wherein the precast cylindrical bodies are sequentially connected to one another in a horizontal direction in a horizontally orientated state, or sequentially connected to one another in a height direction in a vertically oriented state.

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